There is currently a great deal of interest in molecular layer deposition for nano-featured devices, including semiconductors and microelectromechanical systems (MEMS). Rapid and preferably quantitative deposition of single molecular layers with a minimum of byproducts is desirable. Silicon carbonitride films are of particular interest for a variety of dielectric, passivation and etch-stop applications.
Examples of known systems to produce silicon nitride or silicon carbonitride films include that described in U.S. Pat. No. 4,200,666 using trisilylamine ((SiH3)3N) and an inert gas with optional ammonia; the system of diethylsilane and ammonia in an LPCVD system at 800° C., as described in A. Hochberg et al. (Mat. Res. Soc. Symp, 24, 509 (1991)); and the system of cyclic silazanes and ammonia in a chemical vapor deposition (CVD) process described by B. Arkles (J. Electrochemical Soc., Vol. 133, No. 1, pp. 233-234 (1986)).
More recently, halide-containing precursors such as tetraiodosilane and hexachlorodisilane have been described in U.S. Pat. No. 6,586,056 and by M. Tanaka et al. (J. Electrochemical Society, 147, 2284 (2000)), respectively. Unfortunately, there are operational difficulties associated with the corrosiveness of the precursors, as well as with film contaminants and byproducts.
Another approach is the use of bis(t-butylamino)silane, which produces SiN films of reasonable quality at temperatures as low as 550° C. (J. Gumpher et al., J. Electrochem. Soc., 151, G353 (2004)) or in a plasma-assisted pulsed deposition method as described in U.S. Patent Application Publication No. 2011/0256734. In both cases, there are complications with carbon contamination of films and the high energy requirements of both the thermal and plasma regimes, which are not compatible with substrate stability. A review of other alternative approaches is found in EP 2 644 609 A2, which suggests fluorinated precursors. While such fluorinated precursors theoretically allow lower deposition temperatures, the introduced fluorine frequently affects electrical properties of silicon based structures.
Known cyclic azasilanes contain alkyl (e.g., methyl) or alkoxy (e.g., ethoxy) substitution on the silicon atom (see B. Arkles et al., “Cyclic Azasilanes: Volatile Coupling Agents for Nanotechnology” in Silanes and Other Coupling Agents, Vol. 3, K. Mittal (Ed.) VSP (Brill), pp. 179-191 (2004)). In the primary applications of interest, these compounds are unacceptable because they either contain excessive levels of carbon or introduce oxygen into the film due to substitution at the silicon atom on the ring. Thus, the need for new silicon nitride and silicon carbonitride precursors that deposit silicon nitrides at low temperature has still not been satisfied.